Endometriosis is the ectopic growth of viable endometrium outside the uterus, affecting approximately 7% of females. It commonly affects pelvic structures including the bowel. Perforation of the colon by endometriosis is very rare and the patients generally present with an asymptomatic or painful pelvic mass, often in the left iliac fossa. Our patient presented acutely unwell and her symptoms were more suggestive of pyelonephritis or diverticulitis. We therefore report an unusual cause of acute abdomen. The purpose of the following case report is to elucidate certain diagnostic and therapeutic problems of the disease, concerning both surgeons and gynaecologists. In summary, intestinal endometriosis should be considered in the differential diagnosis of all post-menarche women with episodic gastrointestinal symptoms. A past history of endometriosis or co-existent gynaecological symptoms should increase the index of suspicion, and laparoscopy prior to formal laparotomy should be considered. Our patient, in retrospect, had a history of mild endometriosis, but we feel that this case serves as a reminder of a rare, but important, differential diagnosis of acute abdomen in females.